Boulders as examples of two-stage forms - Landforms and Geology of Granite Terrains - page 105

(d)

Figure 5.21. (d) On Houlderoo Rocks, southern piedmont of the Gawler Ranges, South Australia.

various and varied climatic conditions. The concept, which can be traced back almost two hundred
years, is now widely accepted as a rational and reasonable explanation for these, the most common
of all residual forms developed on granitic rocks.
Boulders are not climatic indicators, as assumed by some earlier workers, who mistook
them for glacial erratics. Some, of course, are of this nature, in the sense that they have been trans-
ported by glaciers, possibly being further rounded in the process. But most granite boulders are
residual in that they remain after the grus and other weathered granite that originally enveloped
them have been evacuated. Boulders can be considered to be convergent forms (or forms of equi-
finality), for though most are the result of two-stage development involving fracture-controlled
subsurface weathering followed by differential erosion of the unevenly weathered mass, the pre-
cise nature of the weathering and erosional processes has varied from place to place and no doubt
also from time to time at the same site. Moreover, some are formed by subaerial or epigene
processes.

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